Firms Build Interest In Internet Banking; Hitting "Critical Mass'; A Salt Lake credit union finds the online service registers on Main Street.(INTERNET & TECHNOLOGY)

Byline: J. BONASIA

Wondering if Internet banking has gone mainstream? Look no further than the Mountain America Credit Union in Salt Lake City.

One-third of Mountain America's members have banked online at least once in the past six months. And these online customers are twice as likely to maintain a credit card, debit card or checking account with the credit union than are offline customers.

Mountain America is one of many smaller financial institutions making big inroads online. The company relies on Digital Insight Corp. to provide Internet banking services for its 160,000 members.

Digital Insight, which sells software to banks and credit unions, is on the front lines of Internet banking. As folks in places like Mountain America move their money online, Digital Insight has racked up six straight profitable quarters.

"We're reaching a critical mass now," said John Dorman, the company's chief executive. "There has been enough of a positive experience for this to hit the mainstream."

The use of Internet banking is expected to grow 19% each year through 2007. By then, more than 50 million American households will bank online, according to Jupiter Media Metrix Inc.